The invention relates to an electrical functional unit, in particular a circuit-breaker, for use in aviation. The functional unit has a housing from which there projects an essentially cylindrical fixing neck which has around its circumference at its free end, which is directed away from the housing, a fine thread onto which a nut can be screwed. The fixing neck bears, at its end that is directed toward the housing, a radially projecting abutment flange with an annular flank as an abutment surface which is normal to the longitudinal axis of the fixing neck. The fixing neck serves for securing the unit in a fixing position, in which it projects through a fastening hole or through a fastening bore of a wall element or panel and can be braced therein against the abutment flange by the screwed-on nut. Such functional units, in particular circuit-breakers, are known, for example, from German Patent DE 2 123 765, German Patent DE 40 40 481 C1, German Utility Model DE 8 904 063 U, U.S. Pat. No. 4,400,677 or Published, French Patent Application FR 2 067 954.
Such electrical functional units, in particular circuit-breakers, are often fixed within a wall element or wall panel by a threaded-neck fastening. Usually located within the threaded neck is a functional part, e.g. an actuating handle or a display device, which projects outward from the housing and can be actuated from the outside or is visible from the outside. For strength-related reasons, the fixing neck here, which forms a separate part and is not integrated in the housing, is formed of a metallic material, e.g. steel, brass or aluminum. These materials are all electric conductors and thus give rise to an insulation problem that requires additional configuration outlays to overcome. Furthermore, the high relative density of the metal parts gives rise to a weight problem that is significant, in particular, in the case of an aircraft. This is because the fixing neck alone forms up to 10% of the overall weight of the functional unit. Nowadays, up to 800 such circuit-breakers are used in a large-capacity aircraft.
Furthermore, the secureness of the threaded-neck fixing on the wall element or wall panel has to meet high strength-related requirements that, so it was thought, up until now, could only be ensured by a metallic configuration of the fixing necks.
It is accordingly an object of the invention to provide an electrical functional unit, in particular a circuit-breaker, for use in aviation which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which are of a relatively lightweight configuration without the strength of the threaded-neck fixing being adversely affected as a result.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electrical functional unit. The functional unit contains a housing and a separate, one-piece, plastic cylindrical fixing neck projecting from the housing. The cylindrical fixing neck has a longitudinal axis, a circumference, a first free end directed away from the housing, and a fine thread disposed around the circumference at the first free end and onto the fine thread a nut can be screwed. The fine thread contains a given core diameter, a nominal diameter, and a fine-thread base having a rounded portion with a radius. The fixing neck has a second end directed towards the housing and a radially projecting abutment flange with an annular flank as an abutment surface being normal to the longitudinal axis of the fixing neck and formed in a region above the second end. The cylindrical fixing neck serves for securing the electrical functional unit in a fixing position, in which the electrical functional unit projects through a fastening bore of a wall element and can be braced therein against the radially projecting abutment flange by a screwed-on nut. The cylindrical fixing neck is connected to the housing in a region between the radially projecting abutment flange and the second end. A thread-free, circumferentially cylindrical shank region is formed coaxial with the longitudinal axis and disposed between the fine thread and the radially projecting abutment flange. The thread-free, circumferentially cylindrical shank region has an external diameter substantially equivalent to the given core diameter of the fine-thread. The thread-free, circumferentially cylindrical shank region has an end with a rounded portion merging with the radially projecting abutment flange. The rounded portion is formed substantially as a quarter-circle arc in cross section. The rounded portion has a radius corresponding to half a difference between the nominal diameter of the fine thread and the external diameter of the thread-free, circumferentially cylindrical shank region. The fine thread merges, without any thread runout, into the thread-free, circumferentially cylindrical shank region by way of the radius of the rounded portion of the fine-thread base.
The replacement, provided by the solution, of the conventional fixing neck, produced from a metallic material, by a fixing neck produced from plastic is only apparently obvious. This is because a considerable strength-related problem is posed by the transitions from the fixing-neck thread into the thread-free, essentially cylindrical shank region and from the shank region into the abutment flange of the fixing neck. These transition regions have a decisive influence on the strength and secureness of the unit fixing on the wall panel or wall element. Tests have shown this. Of considerable importance here are the dimensioning of the external diameter of the essentially cylindrical shank region between the threaded part of the fixing neck and the abutment flange as well as the configuration and dimensioning of the transition region of the thread-free, essentially cylindrical shank region into the abutment flange. The dimensions given in the claims in this respect have proven significant for the increase in strength and thus make it possible for the fixing neck to be produced from plastic instead of the hitherto conventional metallic material.
Producing the fixing neck from plastic makes it possible for the fixing neck to be configured as a single-piece, integral multifunctional component that may thus additionally contain a rotation-prevention device in relation to the wall panel. The rotation-prevention device being formed by a separate, discrete component in the case of the conventionally metallic fixing neck. The insulating covering further provided here serves for shielding in the outward direction of the live inner parts of the electrical functional unit.
In accordance with an added feature of the invention, the thread-free, circumferentially cylindrical shank region has an axial length of at least a sum of radii of the rounded portions corresponding to transition regions from the fine thread into the thread-free, circumferentially cylindrical shank region and from the thread-free, circumferentially cylindrical shank region into the radially projecting abutment flange.
In accordance with a further feature of the invention, an axial protrusion is provided and has a radially outer end that flanks an outer side of the fine thread, and the axial protrusion is disposed with a radial spacing from the fine thread. The axial protrusion functions as a rotation-prevention device that acts in relation to the wall element in an installed position. The axial protrusion device is formed integrally with the cylindrical fixing neck.
In accordance with an additional feature of the invention, the insulating coverings project radially beyond the cylindrical fixing neck on two diametrically opposite circumferential regions of the second end of the cylindrical fixing neck. The insulating covers are positioned within an interior of the housing when the cylindrical fixing neck has been actively installed on the housing. The insulating covers are formed integral with the cylindrical fixing neck and have a planar extent oriented at right angles to the longitudinal axial of the cylindrical fixing neck.
In accordance with another feature of the invention, the cylindrical fixing neck is formed from a plastic material having a high mechanical strength over a large temperature range, and is polyester imide, liquid crystal polymers, tetrafluorethylene/ethylene copolymers, polyphenylene sulfide, polyamide imide or polyimide.
In accordance with a concomitant feature of the invention, the fixing neck is molded onto the housing and the electrical function unit is a circuit-breaker for use in aviation.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electrical functional unit, in particular a circuit-breaker, for use in aviation, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.